1. Field of the Invention
The present invention relates to a pump such as a circulating water pump for use in water supply and discharge facilities and power plants, and more particularly to a vortex prevention apparatus for use in a pump pit for preventing an air entrained vortex or a submerged vortex from being produced when water in the pump pit is pumped by a pump.
2. Description of the Related Art
For pumping water from an open channel that is generally used, as shown in FIGS. 31A and 31B of the accompanying drawings, it has been customary to install a pump in such a manner that a suction port 14a defined in the lower end of a suction bell mouth 14 connected to the lower end of a suction casing (pump casing) 12 is immersed in water in a pump pit 10. When the pump is operated, water in the pump pit 10 is introduced through the suction port 14a into the suction casing 12. In this case, since water around the suction port 14a has a free surface, if the suction port 14a is immersed by a small depth S or water in the open channel flows at a large velocity V, then an air entrained vortex (air entraining vortex) A which is connected from the water surface to the suction port 14a by a vortex filament L may be generated, or a submerged vortex B which is connected from the bottom of the pump pit 10 to the suction port 14a may be generated. The generation of the air entrained vortex A or the submerged vortex B tends to cause vibration and noise which are detrimental to the operation of the pump.
As shown in FIGS. 32A and 32B of the accompanying drawings, a water discharge pump is combined with a lateral-suction closed-type channel and has a suction casing 12 having a suction bell mouth 14 placed in a closed-conduit pump pit 10 which has a laterally open inlet port 10c. Since water around the suction port 14a of the suction bell mouth 14 connected to the lower end of the suction casing 12 has no free surface, generation of an air entrained vortex is suppressed. However, when water in the channel flows at an increased velocity V, an air entrained vortex A which is connected from the free surface in an open channel to the suction port 14a by a vortex filament L may be generated, and the construction cost of the closed-type channel is high.
FIGS. 33A and 33B of the accompanying drawings show still another conventional pump having a suction casing 12 placed in a pump pit 10. A vortex prevention plate 16 having a semicircular recess 16a surrounding the suction casing 12 is horizontally attached to a peripheral wall 10a of the pump pit 10. An L-shaped vortex prevention plate (splitter) 18 is attached to the peripheral wall 10a and a bottom wall 10b of the pump pit 10. The L-shaped vortex prevention plate 18 extends along the direction of the water flow from a position laterally of the suction casing 12 to a position below a suction bell mouth 14 connected to the lower end of the suction casing 12.
FIGS. 34A, 34B, and 35 of the accompanying drawings show yet another vortex prevention structure including an annular frame 152 mounted concentrically on the lower end of a suction pipe 150 by support rods 154. The annular frame 152 has a diameter greater than the diameter of the suction pipe 150. The annular frame 152 extends across water flows 156 in a water channel which are directed toward a suction port 150a defined in the lower end of the suction pipe 150, for thereby producing a turbulent layer 158 which extends from the frame 152 to the suction port 150a to prevent an air entrained vortex from being produced.
FIGS. 36A and 36B of the accompanying drawings show still another vortex prevention structure. The vortex prevention structure comprises an inlet water channel casing 160 in the form of a rectangular box having a laterally open inlet port 160a and an upwardly open connection port 160b and defining a closed water channel 162 therein. The inlet water channel casing 160 is placed in an open-type pump pit 10 in such a manner that the inlet port 160a is directed upstream, and the connection port 160b is joined to the suction port 14a of the suction bell mouth 14.
With the conventional arrangement shown in FIGS. 33A and 33B, it is necessary to attach the vortex prevention plate 16 and the splitter 18 to the peripheral wall 10a and the bottom wall 10b of the pump pit 10 and install them in the pump pit 10. Therefore, a civil engineering work is needed to install the vortex prevention plate 16 and the splitter 18, and hence the construction cost of the arrangement shown in FIGS. 33A and 33B is very high. Furthermore, it is very difficult to add the vortex prevention plate 16 and the splitter 18 to the peripheral wall and the bottom wall of an existing pump pit.
With the conventional structure shown in FIGS. 34A, 34B and 35, if a vortex filament extending from the water surface where an air entrained vortex is formed to the suction port passes through a portion near the inside of the frame 152, like a vortex filament 2A, the vortex filament 2A is disturbed by a turbulent layer 158 of wake flow produced by the frame 152, and hence the air entrained vortex becomes unstable and tends to collapse. However, since the air entrained vortex is produced so as to avoid the frame 152 as an obstacle, a vortex filament 1A extending from a portion near the suction pipe 150 to the suction port 150a and a vortex filament 3A extending from a portion outside of the frame 152 to the suction port 150a are mostly produced at positions away from the frame 152. Therefore, the vortex filaments 1A, 3A are hardly affected by the turbulent layer 158, and hence the vortex prevention capability is presumably small.
The conventional structure shown in FIGS. 36A and 36B can suppress the generation of air entrained vortexes at the free surface to a certain extent because the distance from the suction port 14a to the free surface is long and the velocity of water flowing through the inlet port 160a is considerably lower than the velocity of water flowing through the suction port 14a. If the velocity V of water in the channel increases, then there arises an air entrained vortex A which has a vortex filament L extending from the free surface to the suction port 14a through the inlet port 160a and the closed water channel 162.
It is therefore an object of the present invention to provide a vortex prevention apparatus which is capable of preventing air entrained vortexes from being generated in a pump pit with a relatively simple arrangement, without requiring a civil engineering work.
Another object of the present invention is to provide a vortex prevention apparatus which is capable of preventing air entrained vortexes from being generated in a pump pit with a relatively simple arrangement, even if water flows in a water channel at an increased velocity.
According to an aspect of the present invention, there is provided a vortex prevention apparatus comprising: a suction member disposed in an open water channel and having a suction port; and an auxiliary flow-path forming structure disposed substantially concentrically around the suction member with a gap defined between the auxiliary flow-path forming structure and an outer circumferential surface of the suction member, the auxiliary flow-path forming structure defining an auxiliary flow path.
With the above arrangement, a water flow directed from a water surface side toward the suction port is divided into a main flow and an auxiliary flow along the auxiliary flow path, so that locally intense downward flows which is a cause of an air entrained vortex will not be produced. A vortex prevention capability is achieved simply by placing the auxiliary flow-path forming structure or member around the suction member. Therefore, it is not necessary to perform a civil construction work to attach a vortex prevention structure in a pump pit. Therefore, the pump pit may be of a simple rectangular reservoir structure, and hence can be constructed at a low cost.
The auxiliary flow-path forming structure is disposed substantially horizontally over the suction port and spaced therefrom by a predetermined distance.
The auxiliary flow-path forming structure is mounted on the suction member by a plurality of ribs disposed at spaced intervals in a circumferential direction of the auxiliary flow-path forming structure. The ribs are effective in circumferentially dispersing flows which are directed from a portion near the water surface toward the suction port and are a cause of air entrained vortexes. The ribs can provide an increased vortex prevention capability.
The auxiliary flow-path forming structure comprises a plurality of divided members disposed in surrounding relation to a substantially entire circumferential surface of the suction member or a given position of the suction member.
The divided members are radially movably supported on the suction member. For giving a vortex prevention capability to an existing pump, the auxiliary flow-path forming structure is contracted radially inwardly and inserted into a pump installation opening. Then, the auxiliary flow-path forming structure is spread radially outwardly. Therefore, the auxiliary flow-path forming structure which is of a diameter larger than the dimension of the pump installation opening is disposed around the suction member.
The auxiliary flow-path forming structure comprises a ring-shaped pipe.
The pump vortex prevention apparatus further comprises a swirling flow prevention plate mounted on at least one of upper and lower surfaces of the auxiliary flow-path forming structure, and extending vertically and linearly along a water flow. Even when a swirling flow which is a cause of generating a vortex is produced around a pump, the swirling flow is suppressed by the swirling flow prevention plate, thus preventing air entrained vortexes and submerged vortexes from being produced.
The auxiliary flow-path forming structure is of a substantially cylindrical shape disposed around the suction member and spaced therefrom by a predetermined distance.
The pump vortex prevention apparatus further comprises a disk-shaped auxiliary top plate having a hole and disposed above the auxiliary flow-path forming structure with a gap defined between the disk-shaped auxiliary top plate and the auxiliary flow-path forming structure. The disk-shaped auxiliary top plate is effective to prevent a surface vortex from being produced at a position immediately above an inlet of the auxiliary flow path, thus causing a vortex passing through the auxiliary flow path to collapse.
The pump vortex prevention apparatus further comprises a second auxiliary flow-path forming structure disposed concentrically around the auxiliary flow-path forming structure with a gap defined between the second auxiliary flow-path forming structure and the auxiliary flow-path forming structure, the second auxiliary flow-path forming structure defining a second auxiliary flow path.
The auxiliary flow-path forming structure has a wing-like cross-sectional shape for developing a velocity difference between flows along opposite surfaces thereof. The wing-like cross-sectional shape prevents foreign matter from being attached to an upper edge of the auxiliary flow-path forming structure.
The auxiliary flow-path forming structure is mounted on the suction member by a plurality of ribs disposed at spaced intervals in a circumferential direction of the auxiliary flow-path forming structure.
Each of the ribs has an arcuate transverse cross-sectional shape extending in one direction. The arcuate transverse cross-sectional shape of the rib imparts a circumferential pre-swirling flow along the rib to prevent a submerged vortex from being produced.
The vortex prevention apparatus further comprises a bent guide integrally joined to a lower end of the auxiliary flow-path forming structure, the bent guide being curved toward the suction port. The bent guide guides an auxiliary flow to be introduced smoothly into the suction port, resulting in a reduced inlet loss at the suction port.
The vortex prevention apparatus further comprises a pump mount base having a plurality of vertically extending flow-rectifying ribs, the auxiliary flow-path forming structure being disposed between the vertically extending flow-rectifying ribs. Whereas the auxiliary flow-path forming structure prevents an air entrained vortex from being produced, the flow-rectifying ribs which serve to rectify water flows suppress a swirling flow around the pump.
The pump vortex prevention apparatus further comprises a disk-shaped inflow amount adjusting plate having a hole and mounted on an upper end of the auxiliary flow-path forming structure. Since the amount of water flowing into the auxiliary flow path is adjusted by the disk-shaped inflow amount adjusting plate, a large amount of water is prevented from flowing into the auxiliary flow path, and hence an air entrained vortex is prevented from being produced in the auxiliary flow path.
The auxiliary flow-path forming structure comprises a plurality of divided members disposed in surrounding relation to a substantially entire circumferential surface of the suction member or a given position of the suction member.
The divided members are radially movably supported on the suction member.
According to another aspect of the present invention, there is also provided a pump vortex prevention apparatus comprising: a suction member disposed in an open water channel and having a suction port; an auxiliary flow-path forming structure disposed substantially concentrically around the suction member with a gap defined between the auxiliary flow-path forming structure and an outer circumferential surface of the suction member, the auxiliary flow-path forming structure defining an auxiliary flow path; and a suction cone disposed below the suction port. Whereas the auxiliary flow-path forming structure prevents an air entrained vortex from being produced, the suction cone prevents a submerged vortex from being produced.
According to still another aspect of the present invention, there is also provided a pump vortex prevention apparatus comprising: a suction member disposed in an open water channel and having a suction port, the suction member having at least one through hole; and an auxiliary flow-path forming structure disposed substantially concentrically around the suction member, the auxiliary flow-path forming structure being fixedly mounted on a free end of the suction member. The through hole defines an auxiliary flow path. Since no ribs are required to fix the auxiliary flow-path forming structure, the pump vortex prevention structure is simplified in structure.
According to yet another aspect of the present invention, there is also provided a pump vortex prevention apparatus comprising: an inflow water channel structure defining a closed inflow water channel having a laterally open inlet port; and a flow-rectifying plate disposed above the inflow water channel structure and extending upstream of the inlet port in covering relation to the inlet port, the flow-rectifying plate being disposed substantially horizontally and spaced by a predetermined distance from an upper end of the closed inflow water channel structure.
With the above arrangement, shear flows having different velocities across the flow-rectifying plate are produced, and a water flow flowing between the flow-rectifying plate and the inflow water channel structure cuts off a vortex filament interconnecting the free water surface and the inlet port. Therefore, an air entrained vortex is prevented from being produced in the pump pit.
The flow-rectifying plate is inclined to a horizontal plane by an angle in the range of xc2x130xc2x0 for thereby adjusting the water flow flowing between the flow-rectifying plate and the inflow water channel structure and cutting off a vortex filament interconnecting the free water surface and the inlet port.
The flow-rectifying plate has a front edge progressively inclined along a water flow toward opposite ends thereof. Therefore, any foreign matter such as strings attached to the inclined front edge can easily be removed.
The vortex prevention apparatus further comprises a plurality of vertical plates disposed between the inflow water channel structure and the flow-rectifying plate and extending substantially vertically along a water flow, at least one of the vertical plates extending above the flow-rectifying plate. By pre-assembling the vertical plates, the flow-rectifying plate, and also the inflow water channel structure at the factory, the flow-rectifying plate can easily be installed in position. The vertical plate extending above the flow-rectifying plate makes it difficult for a swirling flow to be produced around the pump and above the inflow water channel structure.
Each of the vertical plates is inclined to a vertical plane along the water flow by an angle in the range of xc2x130xc2x0 for thereby adjusting the water flow flowing between the flow-rectifying plate and the inflow water channel structure and cutting off a vortex filament interconnecting the free water surface and the inlet port.
Each of the vertical plates has a front edge progressively inclined downwardly along the water flow. Therefore, any foreign matter attached to the inclined front edge can easily be removed.
The vortex prevention apparatus further comprises a swirling flow prevention plate extending vertically and disposed between a rear end of the inflow water channel structure and a rear wall of the closed inflow water channel. The swirling flow prevention plate makes it difficult for a swirling flow to be produced around the pump, even if the gap between the rear end of the inflow water channel structure and the rear wall of the water channel is large.
The closed inflow water channel structure is detachably connected to a pump suction port.
The inflow water channel structure comprises an elbow-type suction casing. With this arrangement, no water discharge pump needs to be installed on the bottom of the pump pit, and no vortex prevention structure is required to be installed in the pump pit.
The vortex prevention apparatus further comprises a vertical partition wall for partitioning a pump pit, and the inflow water channel structure comprises a horizontal partition wall extending substantially horizontally to an upstream side and joined to a lower end of the vertical partition wall.
The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.